The prequel for Paolo Bacigalupi‘s The Water Knife is now playing out in California’s Central Valley. California’s Water Knives have targeted the Central Valley irrigation districts supplying farmers with water for irrigating crops. The Byron Bethany and West Side Irrigation Districts are some of the first targets of the State Water Resources Control Board’s Water Rights Enforcement Program (the “Cali” Water Knives in Bacigalupi’s novel). Byron Bethany Irrigation District supplies water to about 29,000 acres of farm land and have 100-year old water rights that give them legal access to water from the local rivers/canals. They are now facing up to $5.1 million in fines from the State Water Board for using that right, which the Board has negated. The Water Boards power is based on laws passed by the California legislature that identified “reasonable use” as a limitation to water rights. According to the State’s attorneys the reasonable use of cities trumps Byron-Bethany’s rights. As you might expect, Byron-Bethany’s attorneys have a different view of what is reasonable use of the water they have had a right to use for farming for a century.

One problem is that what is considered reasonable changes through time and is determined by the Water Board and the courts. Growing food, once considered a premier reasonable use is now being replaced by the needs of California’s other water users. Farmers/irrigation districts holding senior water rights are losing their water. Farms are shutting down production because of the lack of irrigation water. Such curtailments directly cost California agriculture $1.5 billion and 17,100 jobs in 2014, and are expected to cost another $1.8 billion and 14,500 jobs in 2015. All together the last two years of drought will cost the total California economy nearly $6 billion. This year, water allocations to Central Valley farmers have fallen by 33% of normal use. This has resulted in nearly $1 billion in extra pumping costs, largely to pay for groundwater to replace the surface water supplies, which is rapidly depleting California’s groundwater reserves. When groundwater supplies are gone, farmers will have no leeway to deal with the Water Board’s cuts. More will go out of business.

Although the present multi-year drought has allowed/forced (depending on your view of government) the Water Board to unsheathe their Water Knives, the problem is much bigger. Water rights holders in California have rights to over 500% of the natural supplies of surface water. So, legally, they could suck out all the water from nearly all the rivers in California. Exacerbating the problem, water demand continues to grow as California’s population expands relentlessly–in 2050 there will be 60 million people in California, there are now 38 million. The California Department of Water Resources predicts that by 2050, under current trends, urban water use will increase by about 50%, while agricultural water use will decrease by about 10% (California Water Plan). The many more people in cities will have much less food produced in California to east, as will others across the country (Farm Press; US Ag).

The Water Board will be the overlord managing these demands. They will move water from farmers to urbanites/suburbanites using the courts. Prof. Buzz Thompson of Stanford Law School predicts that California will win the fight to cut water use and develop a “new way of allocating water”, that will bypass the present water rights system. These legal actions will take many more “Cali Water Knives” managed by the Chair of the Water Board. In the near term, those Water Knives will be “…attorneys and engineers.“, but that will change. Supplies will dwindle, demands skyrocket, and desperate water rights holders who have run out of legal options will physically fight back. Expect to see lawyers replaced by enforcement agents like Paolo Bacigalupi’s ruthless Water Knife, Angel Velasquez, and the Water Board Chair to resemble the authoritarian Catherine Case. To visit that dystopian water future all you have to do now is read “The Water Knife”. You will not have to buy the prequel, because you are living it–just read the news.

The drought in California is big news these days, prompting the N.Y. Times to run an in-depth series on “The Parched West” and far-reaching effects of California’s lack of water. Also in the news was a March 12, 2015 OP Ed in the L.A. Times, in which Jay Famiglietti of NASA contends that California “…has only about one year of water supply left in its reservoirs, and our strategic backup supply, groundwater, is rapidly disappearing.”, conjuring visions of Californians laying next to their empty swimming pool, desperately sucking on their garden hose to get one last drop of moisture. Although there are lots of such apocalyptic news stories, it is not likely that California will dry up and become another lost civilization any time soon. But, it is under serious economic, social and environmental stress from the drought. So, serious that the Governor of California, Jerry Brown, recently instituted mandatory water cuts of up to 36% for some water profligate communities and is now calling for fines of $10,000 for water use violations. Governor Brown has said that the drought is not likely to end soon, and that this is the “new normal” for California. But why should people not living in California care about California’s water woes? Surely Coloradans, Utahans, Washingtonians, New Yorkers, and the Chinese, have no stake in the water wars of California. Why not let California dry up, watch those determined desert sands fill up the emptied swimming pools, and we all can get on with our lives without the constant whining from Californians about “their” drought? (For example, see S. Johnson’s pointless essay, “Apocalyptic Schadenfreude”).

Well, there are plenty of reasons, because unlike Las Vegas, what happens in California does not stay in California. California’s tentacles extend far across the globe, reaching into economic, social and environmental realms. Non-Californians should care, because in some way, small or large, how California responds to this present drought will play out across time and space in our highly interconnected and complex world. To understand those interconnections and why California is so important, we would need to dig deep beneath the surface of the headlines and taglines. But, most importantly, at least for this post, is that “The California Drought” is only an extreme indicator of a much broader problem, “The Not-Just-California Drought” with much bigger implications for future water use in the United States.

Although the news media has concentrated on California, the recent drought covers much of the western United States (Figure 1). Overall, it has directly affected over 64 million people. The drought is also long lasting, especially in California, where a persistent dryness has lasted for over 15 years (Figure 2). (Note: Check out this website on the hydrologic effects of the California drought at http://cida.usgs.gov/ca_drought/.)

Figure 1: Drought across the United States on April 29, 2015. From the NOAA U.S. Drought Atlas

The perception by water managers is that this drought will not end soon. In a 2013 survey, forty state water managers said they expect water shortages in their states over the next 10 years, even if conditions return to “normal” (GOA 2013). With less precipitation and continued population growth and more water demand, managers expect the situation to worsen, not improve. There are several indicators that drought could be a common feature in the western U.S., not just a short interlude. The first is the record of droughts captured in tree rings; the second is future projections from climate models.

Tree Ring Circus

As trees grow they record the presence of drought years in their yearly growth rings. During wet years trees grow well, producing thick rings; during dry years, when growth is stunted, rings are thin (there are complications that we will not worry about now). Many tree-ring studies over the past have shown that prehistoric droughts of many decades are a common feature of the climate (Figure 3), including two “megadroughts” that lasted for over a 200 years each. The most recent tree-ring research applicable to the California drought was published at the end of last year (Griffin and Anchukaitis, 2014).

These researchers found that, “The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.” But, and this is important, they also found that droughts about as severe as the present one were very common in the tree-ring record. Over the last 1200 years, 37 severe droughts lasted for at least 3 years. Even scarier, they found over sixty periods substantially drier than average that lasted for 3 to 9 years. They conclude that, “the climate system is capable of natural precipitation deficits [i.e., droughts] of even greater duration and severity than has so far been witnessed during the comparatively brief 2012–2014 drought episode.” Based on this prehistoric record of past climate, it is likely that we are in for more and longer droughts and maybe even a megadrought. Not a comforting thought.

Figure 3: Time series of the Palmer Drought Severity Index (PDSI) for the last two millennia in California and Nevada. Positive values are wetter, negative values are drier, zero is “average” conditions. The two major “megadroughts” are shaded in pink. From the N. Y. Times.

Crystal Ball

Even less comforting—although not as certain—are climate model predictions of future climate. There have been many previous analyses of California’s future climate using global climate models. These are huge packets of computer code designed to simulate Earth’s present climate. Their forbearers are the weather models that meteorologists use to predict the weather. The difference is that the major controls on Earth’s climate, like greenhouse gas effects, can be modified in global climate models to “look” into the future. In the last decade global climate models have been “downscaled” to cover smaller regions, to predict future climates for say, the southwestern United States. These models, in general, predict a future climate for California, that is hotter and possibly even more varied—larger droughts and floods.

In 2014, four researchers (Ault et al. 2014) found that in the southwest U.S., decade long droughts may be much more common in the future under the highest warming scenario. This year, researchers used a large database of drought index combined with downscaled climate model output to calculate the potential for future drought (Cook et al. 2015). They found that droughts in the southwestern U.S. will likely exceed the driest episodes in the last 1000 years (Figure 4). If these simulations are correct, over the next 85 years California and the surrounding southwest U.S. region may inexorably move into persistent drought conditions.

This is a daunting prospect for the California water system considering how stressed it is under the present drought. Others in the southwest should not be too smug though, for their time is very likely coming, which if you live in Texas is pretty obvious.

Figure 4. The long-term trend of the Palmer drought severity index (PDSI, vertical axis) from 1000 CE to the present and then future projections based on downscaled climate models. Positive values of PDSI are wetter and negative values are drier. Zero is “normal” conditions. From Cook et al. (2015).

Over the Thanksgiving holiday I read a very interesting paper in the journal Nature by J.M Gray and six co-authors (citation at end of article). The article was about the seasonal changes in carbon dioxide in the atmosphere. The iconic curve of increasing CO2 concentrations in the atmosphere is a common figure in many discussions about human-induced climate change. But instead of revisiting the relationship between burning fossil fuels (red line in Figure 1 below), let’s look at another interesting aspect of the CO2 curve that Gray et al. published on in Nature–”seasonality”. (I will wait to talk about what Gray and his colleagues found in another post.)

The black squiggly curve in Figure 1 above shows atmospheric CO2 concentrations averaged over each month. The amplitude of the “squiggles” are controlled by latitude (Figure 2), with higher northern latitudes showing the largest amplitude, and higher southern latitudes showing the lowest amplitude. What would cause such a change? Let’s look in more detail.

If we zoom in on the Mauna Loa data at a higher resolution (daily) and just for one year (2015), we can see that the “squiggles” are actually seasonal cycles (Figure 3). The highest values are in May and the lowest in September. Now we have to think about what would cause the CO2 concentrations to change during the year. Humans add CO2 to the atmosphere at roughly constant rates throughout the year (red line in Fig. 1). That continuous addition causes the upward trend in the CO2 time series. This relatively smooth increase matches the fossil fuel emission curve (Figure 1, red line), but not the seasonal cycle. It turns out that, the seasonal squiggle is caused mostly by land plant growth and senescence during the year (ocean processes also play a role, but not as strong as terrestrial processes). During the growing season, photosynthesis uses CO2 in the atmosphere, decreasing concentration. When plants slow/stop photosynthesizing in the fall, respiration takes over (mostly by microbes in the soil eating plant detritus–“rotting”) producing CO2. Atmospheric CO2 concentrations are controlled by these seasonal processes, in Mauna Loa (and on average globally) peaking in about May and falling to a nadir in about September (Figure 3). Now, let’s return to Figure 2, and have a closer look.

Note again in Figure 2 that the strength of the seasonality of CO2 decreases with more southernly stations: The farther south the station is, the smaller the swing in CO2 over a year. This results from the larger proportion of land in the northern hemisphere. In the northern hemisphere, there are more plants to photosynthesize and remove CO2 from the atmosphere and more plant detritus to rot to add CO2 to the atmosphere (Figure 4). But, if we look closely at different sites we can see some subtleties to these controls.

Let’s compare Pt. Barrow, Alaska, (way up on the North Slope) and the South Pole (as far south as you can get)(Figure 5). Note first that the seasonality is reversed–the two curves are mirror images of one another! So, although the northern hemisphere has the dominant control on global averaged CO2 seasonality, latitude still controls seasonality at a particular site. Pt. Barrow CO2 is maximum Dec-Jun (NH winter and spring), then falls to a minimum Jun-Sep (NH summer ), rising again Sep-Dec (NH fall) to the NH winter maximum. The South Pole is the opposite, controlled by the SH seasons, not the NH seasons.

So, every winter, which ever hemisphere you are in, you will be greeted by higher concentrations of CO2 in the atmosphere. And each year the values climb higher than previous years because of the continuous addition from humans. But, what about that Nature paper I started this post with? Well ran out of space for that in this post and we had to understand carbon dioxide seasonality before we can delve into it. It is really interesting, so I will continue that discussion in the next post–hopefully before the end of the year! In the next post, I will look at if this seasonality is changing over time along with the concentrations. What do you think? Citation: Direct human influence on atmospheric CO2 seasonality from increased cropland productivity, Josh M. Gray, Steve Frolking, Eric A. Kort, Deepak K. Ray, Christopher J. Kucharik, Navin Ramankutty & Mark A. Friedl, Nature 515, 398–401 (20 November 2014) doi:10.1038/nature13957.

November has given us inclement weather across much of the United States. We can use our climate links to visualize how different this weather is from the climate normals I discussed in a previous post. I make those comparisons from Missoula, MT, my home, but you can explore the sites and examine how this year is playing out climatically for you hometown.

Temperature is the big story, with major polar/arctic higher pressure systems defending across the central U.S. Here is a plot of temperature for Missoula for November showing a background of normal and record temps.

You can see that until November 9th, everything was “normal”, maximum and minimum temperatures within or close to the boundaries of the normal band (light green band). In fact there were several days in the “warmer than normal” category. But then everything changed!. On November 10th, a new weather system set up, bringing in the arctic air mass and its associated cold temperatures. For eight days maximum temperatures did not reach or barely reached the normal minimum temperatures. The last two days have warmed some, but with maximum temperatures still well below the normal maximum temperatures. Now, November 21st, the weather has shifted (see Prof. Cliff Mass’ blog for today for a great description of this change in weather) and warmer weather is arriving for the weekend, along with more precipitation.

November precipitation has also been interesting (as those living in Buffalo, NY know!). Here is the same NOAA Weather Service plot for Missoula.

Precipitation for November in Missoula, MT. Thin light green band, near the bottom is normal precipitation; pink is the record for each day.

Not many days of precipitation, but what we had was near record levels. Not that the precipitation came as the warmer weather of early November was replaced by the cold arctic air of middle November. This was due to warm, wet air from the Pacific hitting the arctic blast on November 9 and 10. Let’s look at how all this compared to temperature and precipitation throughout the year. Again, you can get all these plots for you area by going to the NOAA website listed in the precipitation plot or reading the “Normal vs. Normals” post.

Here is the summary for the year, to put our November weather in the annual climate context. Quite something!

First, check out temperature. November really stands out for the year. A blob of low temperatures well below the normal band, but it was not alone. Back in February and early March we had the same sort of arctic blast. But, look at how the precipitation responded to that event versus now.Until mid-February, Missoula precipitation was below normal. Then in omen storm associated with two Feb-Mar weather events, precipitation rose well above normal. Through the Spring precipitation continued to be above normal until Fall, when we entered a dry spell. That was ended by the mid-November storm system that moved through. So, we are now above normal precipitation. That Feb-Mar event also set us for an above normal snow year, that looks to be entrenched for the rest of the year. In fact the NOAA forecast is for substantial snow in Montana’s mountains over the next 72 hours. So, most of November will be subnormal for temperature and supernormal for precipitation. The climate point to all of this? Weather controls these short-term deviations from climate which is a function of “averaging” all this variability.

A common refrain in the climate change literature, both popular and professional, is the impending doom of human society by human-induced global warming. A temperature threshold is even suggested that will tip the world into “dangerous climate change”: 2°C (3.2°F) over pre-industrial temperature, “an upper limit beyond which the risks of grave damage to ecosystems, and of non-linear responses, are expected to increase rapidly”. The U.S. National Research Council claims that such a threshold hasbeen passed and “animals and other species are already struggling to keep up with rapid climate shifts, increasing the risk of mass extinction that would rival the end of the dinosaurs.” But, this has not always been the view of scientists working on the climate. Not long ago geologists thought that the Earth was headed into another ice age, and that very soon humans might be in danger from advancing ice, not thawing ice. (Some researchers still think this).

In the mid 20th Century, there was renewed interest in the origin of the Pleistocene “ice ages”, which waxed and waned between about 2.6 million and 12,000 years ago. During the Pleistocene large, miles-deep ice sheets covered most of northern Europe and northern North America (see figure below).

Deposits left from these glaciers, recorded several ice advances and retreats. But the exact number and timing of these cycleswere poorly known. Then in the 1950s and 1960s new tools were discovered that unlocked the details of the ice ages. One scientist who’s researchfundamentally changed how we think about ice ages, was Cesare Emiliani. Emiliani examined tiny fossils called foraminifera (termed “forams” for short). Forams construct a tiny shell out of calcium carbonate (similar to chalk) by extracting calcium and carbonate from seawater. So, their shells mirror the composition of seawater at the time they lived. When forams die and settle to the ocean bottom theyrecord seawater composition over time as sediment builds up. Emilani discovered that he could use the signature of oxygen isotopesin forams to measure past ocean temperatures. (I will leave the details of this for a later post, it is somewhat complicated.)

Using these tiny “paleothermometers”, Emiliani was able to construct a much more detailed picture of Pleistocene ice sheet advance and retreat. (link to paper). He found numerous glacial advances and retreats over hundreds of thousands of years. He also correlated advances and retreats to the amount of the sun‘s radiation hitting the Earth (termed, insolation) in the Northern Hemisphere. Insolation is fundamentally controlled by changes in the tilt of the Earth’s axis, the shape of its orbit, and the precession of the equinoxes, what are termed “orbital parameters”.In 1966, Emiliani used these relationships to predict a coming glacial event: “…it is to be expected that a new glaciation will begin within a few thousand years and reach its peak about 15,000 years from now.” (figure below left; link).

Changes in ocean temperature calculated by oxygen isotopes by C. Emiliani (1966). Stages on right refer to different “ages” during the Pleistocene. Notice the large changes in temperature between glacial advances (colder) and retreats (warmer).

During the late 1960s and early 1970s other geologists looked at the newly-precise Pleistocene record and came up with similar predictions. In 1972, George Kukla summarized an international workshop on the subject: “It is likely that the presentday warm epoch will terminate relatively soon if man does not intervene”. And, theNational Science Board found: “Judging from the record of the past interglacial ages, the present time of high temperatures should be drawing to an end, to be followed by a long period of considerably colder temperatures leading into the next glacial age some 20,000 years from now.” These views were based on the new understanding at the time of glacial cycles but were also spurred on by new global records of climate becoming available through better climate instrumentation. One of these instrumental records was for temperature. What it showed in the mid 1970s was a strong decrease in temperature over the last 40 years.

This trend combined with the new insights about the ice ages, lead to cautious predictions of continued cooling by many scientists, including those working for the NOAA. This research first made widespread public attention when it was summarized in a story in Time on June 24, 1974 titled “Another Ice Age?”. This article presented a map of increasing ice and snow cover in the Arctic, some of the first data from newly launched environmental satellites. Then a year later, “The Cooling World” was published in Newsweek on April 28, 1975. This article showed a global map of mostly cooling temperatures and a time series of global temperature showing the sharp drop in temperature after 1938 (as shown in the figure below).

Although these articles are now commonly presented as poor journalism because they do not fit our current view of global warming, they were not. They were mostly accurate accounts of what many scientists thought and had published at the time.

Now let’s fast forward to 2014. Forty years after the Time article on the coming of another ice age, we have a much deeper understanding of the length, magnitude and duration of Pleistocene glacial cycles. Let’s look at a couple of relative new articles to see what has changed. First, a paper in 2012 by P.C. Tzedakis from University College London and four co-authors (link here). Tzedakis and his co-authors found that if CO2 concentrations did not exceed 240 ppmV (they are now about 390 ppmV) our current interglacial would end in about 1500 years, followed by another glacial advance. They used both patterns of past interglacials matched to the isolation cycles for our present interglacial and adding ocean processes transporting heat to make their comparisons. Their conclusion was that humans have now added too much CO2 to the atmosphere for the next glaciation to occur if glacials and interglacials followed the same patterns and were controlled by the same processes in the late Pleistocene. But how long would that hold up? To start to answer that question we need to look at a paper by Archer and Ganopolski published in 2005 (link here).

Archer and Ganopolski used a climate model to simulate future climates and ice sheet conditions at different concentrations of CO2. They found that the next glaciation could be postponed a very long time if enough CO2was added to the atmosphere. Since the start of the industrial revolution, humans have released a bit more than 300 gigatons (Gt) of excess carbon into the atmosphere. Their model predicted that those concentrations would postpone the start of the next glaciation by about 1500 years. But they found that if we had added about 1000 Gt of carbon (about three times what we have added so far), the next glaciation would be put off for 140,000 year. And if we had burned all the known reserves of fossil fuels, there would not be another glaciation for at least another 500,000 years—the length of their modeling experiments. If these modeling simulations are correct, humans could completely negate the effects of the global processes that have controlled ice sheet advance and retreat for at least the last 2.5 million years by burning all available fossil fuels.

This is a sobering example of how humans have become a major geologic force, rivaling the controls on Earth’s climate originating at a cosmic scale (orbit of the planet)!

While driving along I-15 through the Wasatch Front Megalopolis (see previous post), there are some interesting features. The most obvious is the steep front of the Wasatch Range to the east. This mountain range was uplifted along a large, active fault at the base of the mountains termed the Wasatch Fault (which has some interesting geologic hazard aspects for this rapidly growing area). There are two other interesting features along the front the mountains. One is that prime housing developments (and some fancy golf courses) are very common on a series of flat surfaces (terraces) along the mountain front (see figure below). These have great views of both the mountains and the valley below and so are prime real estate. The terraces are also mined for gravel to fuel development. Terraces are extensive extending along the entire Wasatch Front and beyond around the edges of the Great Salt Lake Valley. The largest and most complex terraces are associated with large canyons or prominent ridges extending out from the range front. What are these features and what can they tell us about the paleoclimate of the Wasatch Front and the role humans play in modifying the Earth’s landscapes?

Terraces (extending from the canyon in the upper right all the way to the left edge of the picture) along the Wasatch Range front. There terraces support housing developments (left center) and gravel mines (center). This image is from above Cottonwood Heights, UT, looking towards the east. Image from Google Earth, 2013.

To answer that question we need to go back to the mid-late 1800s and examine the work of one of the West’s most famous Geologists, Grove Karl Gilbert. In 1890, G.K. Gilbert (as he is mostly known) published a report on a large prehistoric lake that filled the Great Salt Lake basin thousands of years ago. This work was based on extensive field work he and explorers before him had done in the Great Salt Lake basin. He named the prehistoric lake they discovered, Lake Bonneville, after explorerBenjamin Louis Eulalie de Bonneville (1796–1878), and identified a number of features formed by the lake. At it greatest extent it was over 500 km long, 200 km wide, and 300 m deep filling the Salt Lake Valley. Gilbert found evidence for Lake Bonneville in the terraces seen along the mountain fronts (figure below). He recognized that the basin was filled with a much larger lake during the last part of the geologic epoch called the Pleistocene.

Drawing of Lake Bonneville terraces from Gilbert’s 1890 report.

These terraces and other shoreline features (deltas, spits, tombolos and barrier bars) established that the lake existed for a long time at several different elevation or stands. It remained at some particular elevations for long periods of time (hundreds to thousands or years–first figure below) forming large deposits of sand and gravel. Research since Gilbert’s pioneering work, has dated these stands and established the geologic history of Lake Bonneville and contemporaneous lakes throughout the Great Basin to the east of the Wasatch Range (second figure below).Lake Bonneville and contemporaneous paleo-lakes in the Great Basin are called Late Pleistocene lakes because they were at their high stands during the last part of that epoch. The Late Pleistocene encompasses the last major continental ice sheet advance from about 126,000 year ago to 11,700 year ago. The North American ice sheet reached its maximum southward extent (termed last glacial maximum or LGM) during the Late Pleistocene. The timing of the LGM, about 30,000-17,500 years ago encompassing the time of the high stands of Lake Bonneville. By 15,000-11,500 the Earth was warming and moving into the present interglacial, the Holocene (starting about 11,700 years ago and extending to the present).

The vast extent of Late Pleistocene lakes in the Great Basin and the huge size of Lake Bonneville in particular (and Lake Lahonton on the west side of the Great Basin), show that the climate was very different about 20,000 years ago compared to now. Some researchers think that rainfall in the region needed to be from 140-280% of present values to get high lake stands, while evaporation was likely about 30% lower due to decreased temperatures during glacial times (maybe as much as 5-10ºF). Annual mean precipitation for Salt Lake City is now 16 inches. Late Pleistocene precipitation would therefore be on the order of 23-46 inches, for a average of about 34 inches. The low end is about like that of present-day San Francisco, CA (21 inches), the high about like Tampa, FL (46 inches), and the mean pretty much like Seattle (38 inches). So, Salt Lake City in the late Pleistocene was a fairly wet place compared to now! Let’s now return to the Lake Bonneville shoreline deposits and look at how humans utilize those deposits and what that says about our ability to modify the landscape.

The higher precipitation in along the Wasatch Front lead to higher runoff. More flow in the streams eroded the surrounding mountains transporting sediment into Lake Bonnevile forming extensive shoreline deposits. Strong and persistent winds transported sediments along the shore forming the terraces, spits and beach ridges. Where rivers and streams entered the lake, deltas were formed. As the lake dropped sediment was spread out, forming the present-day deposits. These sediments are unconsolidated so easy to excavate. They are also very close to where all the building is taking place so easy to transport to building sites. So, they make building roads and structures along the Wasatch Front relatively cheap–there is nearly always a gravel bar close at hand to new development. These terrace deposits are the foundation of the Wasatch Front Megalopolis. From 1994-2007 (last date data is available), 287 million metric tons of sand and gravel were extracted in the region along the Wasatch Front (data from U.S. Minerals Information Service, see figure below). The reconstruction of Interstate-15 and associated federal highways in the run up to the 2002 Salt Lake City Olympics used over 12 million metric tons of sand and gravel. Construction of high-rise buildings, Olympic Villages and other associated structures used more, forming the large spike in the plot of sand and gravel mined from 1997-2000 (figure below).

Sand and gravel production from the district that encompasses the Wasatch Front corridor. Data is from the U.S. Minerals Information Services state data (http://minerals.usgs.gov/minerals/).

Now, another boom in building is happening that is not yet completely captured by data provided by the U.S. Minerals Information Service because their last reported data is for 2007 production. In some places the excavation of sand and gravel has removed a substantial proportion of the deposits that formed over several thousand years along the shores of Lake Bonneville. Let’s look at one of those deposits, the Point of Mountain Spit.

Point of Mountain is a spectacular spot just south of Salt Lake City. A high, traverse ridge extends westward several miles from the Wasatch Range separating the Salt Lake Valley from Utah Valley at the Jordan Narrows. Strong shoreline currents carried sediment southward toward this spot, forming a gigantic spit of sand and gravel that extends (extended) from the Salt Lake Valley into Utah Valley. When Gilbert described this spit, it was an intact feature. In 1993 much of the spit was still enact and the shoreline terrace to the north was relatively undeveloped (figure below), but some gravel mining had destroyed the end of the spit (where I-15 curves around the ridge in the figure below), likely to build the first stages of I-15.

1993 oblique view (looking south) of the Point of Mountain Spit and associated shoreline terrace. The lake ward end of the spit is somewhat destroyed by gravel mining (light areas) but the general shape can be seen extending into the gap between Salt Lake Valley and Utah Valley. Yellow outline is approx. extent of spit and other terrace-like deposits.

Twenty years later in 2013, the spit was completely transformed (figure below).

2013 oblique view (looking south) of the Point of Mountain Spit area and associated shoreline terrace. Major excavation and development has modified the deposits. Image from Google Earth.

The entire end of the spit and much of the underlying gravels have been excavated in a huge gravel mine. Even the ends of the mountain ridge has been mined for rock. The shoreline terrace is nearly completely covered with housing developments (the undeveloped end is a paraglider park, so was saved). Much of the farm land in the valley has been transformed to housing developments and roads. This shows the accessibility of Lake Bonneville deposits to the demand for construction materials. Gravel from the spit goes right into adjacent roads, houses, business parks and shopping malls. The figure below is a closer and vertical view that better illustrates the magnitude of these excavations–all of the lighter areas are the sand/gravel/rock mines and roughly outline the previous extent of the spit.

2013 vertical view of the gravel mines at the Point of Mountain Spit. From Google Earth.

Extensive Lake Bonneville deposits like the Point of Mountain Spit probably took from 500-1500 years to form (length of a stand in the lake and following drawdown). Humans have nearly completely excavated it in about 20 years. Or a rate of destruction 25-75 times faster than construction. This shows what a tremendous power direct human actions are in the modern world. Research looking at human actions at the global scale show a similar rate of “human erosion”, about 40 times geologic rates (see “Moving Dirt” in the post archives). Humans now have become the premier mover of material on the Earth’s surface, more efficient than all other geologic processes. The Wasatch Front Megalopolis is a prime example of that ability. In a little over a century we have come a long way in completely transforming a natural landscape that took many thousands of years to develop into a human construct. That is incredible power. Is the next stage Trantor?

I recently drove through the Wasatch Front Urban Corridor (figure below), on my way from western Montana to southern Utah. This roughly 120-mile long corridor is a spectacular example of an emerging megalopolis and the power of humans to modify the Earth. But the Wasatch front also has some interesting climate and paleoclimate (prehistoric climate) features that help explain the development and how past climates can facilitate the expansion of human society.

The Wasatch Front Megalopolis (grey areas with city names), that encompasses Salt Lake City and the various cities to the north and south (north is to the left). The Wasatch Mountains are to the east (top of image); the Great Salt Lake (lower left) and Utah Lake (upper right) to the west. The Wasatch Megalopolis extends about 120 miles along I-15 and is composed of nearly continuos housing developments, shopping malls, business districts, schools, and other associated infrastructure of modern American suburbia/exurbia. From Google Earth imagery, 2013.

The spectacular fault-bounded Wasatch Range on the east and the Great Salt Lake and Utah Lake on the west hem in development along the front. Over 2.3 million people live in this corridor and population is growing fast (table below). About 80% of Utah’s population is concentrated along the Wasatch Front, where about 85% of Utah’s economic productivity is generated. This is an amazing place growth wise!

So, why are all these people coming to the Wasatch Front? There are the usual socio-economic factors for sure (jobs, family, etc), but it is also a good place climatically. To show you, I will use a climate data plotting site called WeatherSpark that I have not introduced yet. WeatherSpark is a website that uses a wide range of available data to make unique graphs of local climate. Many of these differ from those that you can get from the U.S. Weather Service (that I presented in the last post) and add more useful climate parameters. In Part I of this post, I will present the climate of Salt Lake City, in the center of the Wasatch Megalopolis, to show why the Wasatch Front is such a good place climatically (at least for some people). Then in Part II of this post I will explore the recent paleoclimate (prehistorical climate) features of the Wasatch Megalopolis and look at what this all means in the context of humans’ ability to modify the Earth.

OK, now for the recent climate of Salt Lake City, the epicenter of the Wasatch Megalopolis.

Here is a plot from WeatherSpark showing the annual maximum and minimum temperatures for Salt Lake City (SLC). Looks pretty good, as long as you do not mind coolish winters and warmish summers.

The daily average low (blue) and high (red) temperature with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

But how do these temperatures “feel” on average. Here is a plot that can give you an idea:

The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

Not much hot weather and a large amount of warm, comfortable, and cool weather: “not to hot, not too cold, just about right”. At least for some folks. But here is a more useful plot, because in general people seem to like climates without much rain. Here is how SLC stacks up:

The fraction of days in which various types of precipitation are observed. If more than one type of precipitation is reported in a given day, the more severe precipitation is counted. For example, if light rain is observed in the same day as a thunderstorm, that day counts towards the thunderstorm totals. The order of severity is from the top down in this graph, with the most severe at the bottom.

Pretty nice summers, with only a quarter of the days with precipitation, and that mostly in thunderstorms. Snow in the winter, so good for skiing, but still with only 50% of the days with precipitation. But what about “humidity”? It can be not-so-hot, but really humid, so pretty miserable. Here is a WeatherSpark plot of dew point that takes into account temperature and humidity, which can be a better measure of how comfortable the climate is:

The daily average low (blue) and high (red) dew point with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Mostly comfortable summers and feels dry the rest of the year. So, if you like dry and sunny, SLC is for you! But remember, these are “average” conditions (see post on Normal vs. Normals) and not conditions that you will experience every day or even often. That is another nice feature of the WeatherSpark plots, they give you a feel for the spread of each climate parameter. The darker colored bands are the spread between 75th percentile and the 25th percentile, representing central 50%. The lighter colored bands represent 90% of the data. So, you can get a good feel for the spread of the parameter as well as the central tendency.

There is another climate control along the Wasatch Front that makes it a desirable place to live and helps drive the growth of the megalopolis. The steep front of the mountains, just east of the corridor, add a third climate dimension. The Wasatch Range forms a steep elevation barrier to storms arriving from the southwest. Air moving eastward over the mountains, rises and cools. The cooler air cannot hold as much moisture, so it falls as snow or rain (depending on the season). The Great Salt Lake also supplies moisture to the atmosphere through evaporation as winds blow across the lake (called a “lake effect”). These climatic factors lead to heavier precipitation in the mountains than in the Wasatch Front corridor. Looking at the figure below, we can see that the average annual precipitation within the Wasatch Front Megalopolis is about 15 to 25 inches, while in the Wasatch Range, just east it is from 40 to >60 inches. So, people can live in a relatively warmer and drier climate but have quick (depending on traffic) access to deep, dry snow in the mountains to the east.

Because the Wasatch Range snow is deep and dry it makes for excellent skiing so is home to some of the country’s best skiing and other winter sports. Unfortunately, the proximity to the about 2.3 million people of the Wasatch Front Megalopolis also makes it some of the most crowded (and expensive resorts) as well. But, at least for about 2.3 million people in the Wasatch Front Megalopolis, this area has a Goldilocks Effect, “not too hot, not too cold, just right”. For some things that is, but easy driving is not one of them! Nor is living in a natural landscape as the megalopolis gobbles it up. That is the topic of the next post.